The invention relates to a method and apparatus for reducing hydrocarbon emissions from an internal combustion engine particularly during the cold-start phase of engine operation utilizing a catalytic converter and an adsorber.
U.S. Pat. No. 5,051,244, for example, discloses such a method for reducing hydrocarbon emissions. In an exhaust conduit of an internal combustion engine with a catalytic converter there is an adsorber for the adsorption of hydrocarbons upstream of the catalytic converter, the adsorber being arranged in a bypass conduit to the exhaust conduit. Arranged at the exit of the bypass conduit from the exhaust conduit is an on-off valve for controlling a flow connection between the exhaust conduit and the bypass conduit, control being performed, inter alia, as a function of the temperature of the adsorber.
With regard to the general background, attention is also drawn to printed publications DE 39 28 760 C2, DE 42 05 496 C1, 42 07 005 A1, German Utility Model 90 03 204, EP 0 424 966 A1, EP 0 460 542 A2 and JP 2-135126.
A disadvantage of known methods for reducing the hydrocarbon emissions from internal combustion engines is the fact that the desorption temperature of the adsorber is significantly below the operational temperature of the catalytic converter downstream of the adsorber, for which reason undesirably high hydrocarbon emissions occur in certain periods of the cold-starting phase.
It is the object of the invention to provide a method of reducing hydrocarbon emissions in such a way that a significant reduction in hydrocarbon emissions can be achieved also during the entire cold-starting phase of an internal combustion engine.